Electronic tuning type television receiver

Abstract

A television receiver of electronic tuning type employing a variable capacitance diode in a local oscillator of its tuning circuit, which comprises a memory storing a plurality of digital data indicative of tuning voltages corresponding to a plurality of channels respectively so that a tuning voltage corresponding to a selected channel can be applied to the variable capacitance diode in the tuning circuit, a D/A converter converting a digital data corresponding to a selected channel into an analog voltage to be supplied to the variable capacitance diode, and a tuning voltage control circuit which functions to sequentially modify, at a predetermined rate, the digital data of the selected channel read out from the memory until the tuning point is reached in the tuning circuit, and which applies sequentially such a signal to the D/A converter, whereby the tuning circuit can be tuned to the selected channel regardless of secular and other variations in the operating characteristic of the variable capacitance diode.

What is claimed is: 
     
       1. An electronic tuning type television receiver comprising a tuning circuit including a local oscillator whose oscillation frequency is controlled to be variable depending on a voltage applied to a variable capacitance means, signal input means for specifying a selected channel, memory means for storing digital data indicative of tuning voltages corresponding to a plurality of channels respectively so that a tuning voltage corresponding to a selected channel can be applied to said variable capacitance means in said tuning circuit, means for reading out from said memory means the digital data corresponding to the selected channel specified by said signal input means, a D/A converter converting the digital data read out from said memory means to an analog signal which is applied to said variable capacitance means, and a tuning detection circuit for generating a signal when said tuning circuit is tuned to the selected channel, wherein tuning voltage control means are provided for alternately increasing and decreasing, at a predetermined rate, the digital data read out from said memory means to sequentially apply a signal representative of said alternately increased and decreased data to said D/A converter, and for ceasing the increasing and decreasing operation in response to the appearance of an output from said tuning detection circuit. 
     
     
       2. An electronic tuning type television receiver comprising a tuning circuit including a local oscillator whose oscillation frequency is controlled to be variable depending on a voltage applied to a variable capacitance diode, signal input means for specifying a selected channel, memory means for storing digital data indicative of tuning voltages corresponding to a plurality of channels respectively so that a tuning voltage corresponding to a selected channel can be applied to said variable capacitance diode in said tuning circuit, means for reading out from said memory means the digital data corresponding to the selected channel specified by said signal input means, a D/A converter converting the digital data read out from said memory means to an analog signal which is applied to said variable capacitance diode, and a tuning detection circuit detecting the fact that said tuning circuit is tuned to the selected channel, wherein the improvement comprises tuning voltage control means which functions to sequentially modify, at a predetermined rate, the digital data read out from said memory means to sequentially apply such a signal to said D/A converter, and which ceases its data modifying operation in response to the appearance of an output from said tuning detection circuit, and wherein said tuning voltage control means comprises means for generating a train of clock pulses, counter means starting to count said clock pulses under control of said means for reading out the digital data from said memory means, and arithmetic operation means for adding or subtracting the count of said counter means to or from the digital data read out from said memory means, the output of said arithmetic operation means being applied to said D/A converter.   
     
     
       3. An electronic tuning type television receiver comprising a tuning circuit including a local oscillator whose oscillation frequency is controlled to be variable depending on a voltage applied to a variable capacitance means, signal input means for specifying a selected channel, memory means for storing digital data indicative of tuning voltages corresponding to a plurality of channels respectively so that a tuning voltage corresponding to a selected channel can be applied to said variable capacitance means in said tuning circuit, means for reading out from said memory means the digital data corresponding to the selected channel specified by said signal input means, a D/A converter converting the digital data read out from said memory means to an analog signal which is applied to said variable capacitance means, a tuning detection circuit generating a signal when said tuning circuit is tuned to the selected channel, means to generate an alternately varying signal to control digital data being read out from said memory to said D/A converter, means to sequentially change the value of said digital data in accordance with said alternately varying signal, and means responsive to said signal at the output of said tuning detection circuit to cease generation of said alternately varying signal.